Plant and soil nitrogen in oligotrophic boreal forest habitats with varying moss depths:does exclusion of large grazers matter?

• Published in: Oecologia
• Main Authors: Väisänen, Maria, Tuomi, Maria, Bailey, Hannah, Welker, Jeffrey M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2021
• Subjects: Dwarf shrub; Inorganic nitrogen; Reindeer; δ C; δ N; /dk/atira/pure/person/fieldofscience2010/1/18/1; name=Ecology; evolutionary biology; Rangifer tarandus
• Online Access: https://research.ulapland.fi/fi/publications/7cee46a2-a21b-4ed6-a93e-1c5f81f8c3d3; https://doi.org/10.1007/s00442-021-04957-0; https://lacris.ulapland.fi/ws/files/16836864/Va_isa_nen_et_al._2021.docx; http://www.scopus.com/inward/record.url?scp=85107412945&partnerID=8YFLogxK; http://www.scopus.com/inward/citedby.url?scp=85107412945&partnerID=8YFLogxK

The boreal forest consists of drier sunlit and moister-shaded habitats with varying moss abundance. Mosses control vascular plant–soil interactions, yet they all can also be altered by grazers. We determined how 2 decades of reindeer (Rangifer tarandus) exclusion affect feather moss (Pleurozium schreberi) depth, and the accompanying soil N dynamics (total and dissolvable inorganic N, δ 15 N), plant foliar N, and stable isotopes (δ 15 N, δ 13 C) in two contrasting habitats of an oligotrophic Scots pine forest. The study species were pine seedling (Pinus sylvestris L.), bilberry (Vaccinium myrtillus L.), lingonberry (V. vitis-idaea L.), and feather moss. Moss carpet was deeper in shaded than sunlit habitats and increased with grazer exclusion. Humus N content increased in the shade as did humus δ 15 N, which also increased due to exclusion in the sunlit habitats. Exclusion increased inorganic N concentration in the mineral soil. These soil responses were correlated with moss depth. Foliar chemistry varied due to habitat depending on species identity. Pine seedlings showed higher foliar N content and lower foliar δ 15 N in the shaded than in the sunlit habitats, while bilberry had both higher foliar N and δ 15 N in the shade. Thus, foliar δ 15 N values of co-existing species diverged in the shade indicating enhanced N partitioning. We conclude that despite strong grazing-induced shifts in mosses and subtler shifts in soil N, the N dynamics of vascular vegetation remain unchanged. These indicate that plant–soil interactions are resistant to shifts in grazing intensity, a pattern that appears to be common across boreal oligotrophic forests.